Bullet Drop Very Different To Calculator

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Tris88

Well-Known Member
Ok so first thing is first I don’t have a chronograph (yet). Currently thinking I may get one but also wondering if there is a point

I reload my 6.5 Creedmoor with 34gr of N-150 in Peterson SRP brass. Using a hornady 143gr ELD-x seated to the max COL (recommended by hornady) of 2.800” which is 0.091 more than Vhit’s data. Rifle is a Bergara B14 hunter 24” barrel with an evolution wildcat mod 1:8 twist.

I worked up the load for deer so I wanted it to be legal. 34gr was the sweet spot and groups at around 1/2” so I didn’t mess about much more, because why bother if it’s accurate reliably.

I guesstimated that if Vhit’s max load with 34.4gr is shooting at 2503fps that I’d be a bit under this with a 1.5” shorter barrel and slightly less powder. Maybe 2450fps. Punched this into a calculator and got a drop of 5” at 200. Went out to test. It’s 4”. This seems a big difference and if I reverse engineer the calculator it says they are firing at 2650fps. This seems very wrong.

I am new to reloading so perhaps I am flawed in my thinking or are calculators usually out this much? Either way be gentle with me, any advice would be gratefully received.
 
There's no single answer as to why there's such a "variation" in drop.

One inch at 200 yards is 1/2 MOA. How big a group did you shoot? How many rounds? It's possible that you have measured the drop from a round that was at the top of the group, rather than the mean centre. If that's the case, the drop you predicted was in fact correct!

You could shift a group by 1/2 MOA by shooting at a different angle to the "zero".
You could shift a group by 1/2 MOA by having your head on a different part of the stock, inducing parallax error.
You might not have entered all the variables into your calculator correctly. Scope height? Atmospheric pressure? Temperature? Humidity? Most importantly, even if those variables were spot on, the crucial factor is MV, and you don't know what that is!

It's also possible that you have a fast barrel.
Or that your load gives more pressure due to seating depth, or, or, or........

There are far too many variables to guesstimate MV. So my suggestion would be to do exactly as you have done, and go and shoot the round at various distances and record what they actually do. If and when you shoot the rounds over a chronograph you'll be in a better position to work with a ballistic calculator.

Have fun!
 
What are you talking about anyway? Metres or yards? This alone can account for an inch difference.
 
8x57 said:
Forget the computer predictions and just get out there and test it for real. :thumb:
Click to expand...
Beat me to it!

Use the ballistic data to get you on the paper then make a note of things like temp, humidity, altitude, wind, etc & record 'real world data' for your rifle shooting your loads at different distances. Do each distance at the same time & using the same bench/rests so they're directly comparable. I'd also suggest repeating in different conditions, i.e. do a set now then do a set in the summer when its warmer & another set when the temp is lower or it's raining in the winter as you'll get different results.

One thing I am surprised at is that you're only getting 1/2" groups from the Creedmore, from what I have seen posted on here by others I'd thought they were hyper accurate, I get 1/2" groups from my 222Rem in a barrel that's had >15,000 rounds down it, is pitted near the muzzle & using practice ammo I've loaded on a progressive press 😳
 
Whether you use a chrono or not, observing real-world splash/holes-on-target at different ranges is invaluable, but 200m is really too close to tell you enough to true up your ballistic calculator. Also, for reliable predictions at ranges where the drop is significant, recording/inputting the environmental data is vital, so if you don't yet have a Kestrel-type weather station I'd put one on your Christmas list (and then give yourself an early Christmas present). As for reloading without a chronograph, I really wouldn't, as only the chrono can tell you how consistent (SD/ES), as well as how fast (MV) your loads are when you only have a short range to play on (as most of us do most of the time), plus it's a good deal more accurate/precise than trying to work out those issues by diagnosing problems in distant groups that are subject to any number of variables.
 
The bullet doesn't lie...as been said before double check the data your putting in.

If your dmgetting a .5moa at 100m then the 'generic' way of accuracy means 200m will be 1", 300m 1.5" etc so your data may be perfectly within accuracy spec. Plus your rounds may group nicely at 100 but open like a shotgun at 200 or 300m.

I reload and don't use a chrono for data, I just shoot it at range and true the data on the ballistic apps and confirm...job done ✔
 
Clock /walk it around a 1/4/ 1 inch or CM grid with you zero nr the top of a 2x4 foot high grid target see if the clicks match the dope, if not do your own its far better to know your own combo anyway . They test in still air with a setup thats nothing like yours .
A plus is good informative trigger time :thumb:
 
Tris88 said:
Ok so first thing is first I don’t have a chronograph (yet). Currently thinking I may get one but also wondering if there is a point

I reload my 6.5 Creedmoor with 34gr of N-150 in Peterson SRP brass. Using a hornady 143gr ELD-x seated to the max COL (recommended by hornady) of 2.800” which is 0.091 more than Vhit’s data. Rifle is a Bergara B14 hunter 24” barrel with an evolution wildcat mod 1:8 twist.

I worked up the load for deer so I wanted it to be legal. 34gr was the sweet spot and groups at around 1/2” so I didn’t mess about much more, because why bother if it’s accurate reliably.

I guesstimated that if Vhit’s max load with 34.4gr is shooting at 2503fps that I’d be a bit under this with a 1.5” shorter barrel and slightly less powder. Maybe 2450fps. Punched this into a calculator and got a drop of 5” at 200. Went out to test. It’s 4”. This seems a big difference and if I reverse engineer the calculator it says they are firing at 2650fps. This seems very wrong.

I am new to reloading so perhaps I am flawed in my thinking or are calculators usually out this much? Either way be gentle with me, any advice would be gratefully received.
Click to expand...
You've simply discovered the different between theory and reality.
Reality tends to be a more reliable source for making decisions.

Cheers

Bruce
 
Tris88 said:
Ok so first thing is first I don’t have a chronograph (yet). Currently thinking I may get one but also wondering if there is a point

I reload my 6.5 Creedmoor with 34gr of N-150 in Peterson SRP brass. Using a hornady 143gr ELD-x seated to the max COL (recommended by hornady) of 2.800” which is 0.091 more than Vhit’s data. Rifle is a Bergara B14 hunter 24” barrel with an evolution wildcat mod 1:8 twist.

I worked up the load for deer so I wanted it to be legal. 34gr was the sweet spot and groups at around 1/2” so I didn’t mess about much more, because why bother if it’s accurate reliably.

I guesstimated that if Vhit’s max load with 34.4gr is shooting at 2503fps that I’d be a bit under this with a 1.5” shorter barrel and slightly less powder. Maybe 2450fps. Punched this into a calculator and got a drop of 5” at 200. Went out to test. It’s 4”. This seems a big difference and if I reverse engineer the calculator it says they are firing at 2650fps. This seems very wrong.

I am new to reloading so perhaps I am flawed in my thinking or are calculators usually out this much? Either way be gentle with me, any advice would be gratefully received.
Click to expand...

Quite simply the difference could be the consistency of you eye elighnment to the scope , air pressure, your hold during recoil, wind acting on a ground contour , trigger pull etc etc etc.
And you actually guessed important data as in your velocity?
 
Truing up a ballistic curve is a bit of an art form. All the variables of the actual powder burn rate, air and powder temp etc all affect velocity to some degree. The reality is that one of the biggest impacts on the curve down range is the true zero you put in. To get a true zero, you really need the bullet to be dropping, so at least 2-300 yards. You can then work back to what the actual zero is. I'll bet if you change your zero value from 100 to say 120 (which would be a miniscule change on your 100 target) would have a lessening impact on the drop as you experienced. It's far more apparent further out, but you can true a curve out past 1000m against the real data in this manner.
 
Thanks everyone for such useful suggestions.

I am a practical accuracy sort of chap. I shoot at living targets most of the time and have the respect to test ranges first. I’ve usually shot out to a max of 130 yards, some new land has no cover and requires some longer shots up to 200. I am keen to know where my bullet goes. So I’ll be setting up a plethora of targets at varying range to confirm.

I don’t like relying on data without trying it, as so many of you have suggested, I don’t need the chrono because I’ll be testing anyway, an inch is close enough to get me on the paper and fine tune.

To answer some of your questions:
@Mungo five rounds fired at 200yards, pretty confident shooting at or below 1/2” MOA

@Rider both are yards

@8x57 & @Donkey Basher this is definitely the way forward, at least I know where I’m going to place the rounds in reality. When I had the rifle on a bench at the range I shot 1/4” MOA with my 8x56, I could probably dial a bit more accuracy in but do I really need to? 1/2” in the field with my 6x42 seems accurate enough for me.

Thanks again to everyone for your advice, I think I’ll skip the chrono and just use approximation to get me on paper then dial it in with testing on targets in the field.
 
No substitute for ‘dope’ unless you are having to extrapolate to distances for which you can’t build info empirically

This morning I was shooting out to about 200m with my Cz 452.

The Kestral was miles out - both for vertical and wind

Now I expect wind calls to be difficult- they just are

Vertical?

Rubbish in rubbish out - so back to drawing board

Was sprawled over roof of car in order to get the elevation, so I’m sure much of the error occurred as a result of me fidgeting
 
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